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Highly selective transfer of hydrogen sulfide (HzS) from much larger quantities of carbon dioxide (COZ) has been accomplished by absorption and reaction into fine sprays of buffered carbonate solution. Selectivity after the intensely agitated atomization zone is dramatically improved once the droplets have formed and stagnate internally. HZS transfer in this latter zone is virtually independent of the presence of COz, even at C02:HzS ratios of 1cO; COZ transfer, however, is adversely affected by the presence of H2S. The gas film resistance for mass transfer is effectively eliminated with the 50 p m mean droplet diameter. The data indicate approximately constant hydrodynamics throughout the formed droplet zone and allow.good theoretical prediction of enhancement factors for this complex system. Thus the design of more efficient equipment is possible if the gas-liquid contacting method is tailored to take advantage of differences in the transfer and reaction rate properties of gases to be separated. E. BENDALL, R. C. AIKEN, and F. MANDAS Department of Chemical EngineeringUniversity of Utah Salt Lake City, UT 84112The need for a selective separation of HzS from COz occurs as it is often too expensive and not necessary to remove large quantities of COz along with the pollutant HzS. Often no process is capable of removing the H2S to specifications without uneconomical removal of the majority of the COz, thus requiring a large purification plant and large capital investment. Situations in which HZS and larger quantities of COz appear include low to medium BTU gas wells or natural COz sources, and in fossil fuel plants operating under partial oxidative environments.There have been few experimental or theoretical studies of mass transfer into a dispersed medium with subsequent intraphase reaction. Applications include topics in liquid-liquid extraction and gas purification where single components are transferred or multiple competitively or synergistically interacting components are transferred. Description of the fluid dynamics for such systems is complicated by the existence of three different regimes always present: atomization, droplet flight, and coalescence. Many atomization techniques exist and none are welldescribed for sprays. Atomization greatly affects the droplet flight regime as it determines the droplet size distribution, dynamics and interaction. Continuous phase backmixing and internal dispersed-phase mixing further can complicate the theoretical description of the fluid dynamics.This article contains a summary of an experimental study on selective removal of HzS from much larger quantities of COz using a conventional liquid solution but sprayed into a chamber as a fine mist. The primary variable between runs was the amount of liquid reagent in solution. Gas and liquid samples were taken throughout the reactor. CONCLUSIONS AND SIGNIFICANCEThere is a significant increase in selective and extensive transport of H2S over COz if the scrubbing liquid is finely divided. This advantage is particularly great outs...

Simulation studies are presented of single-and two-component adsorption in periodic, countercurrent, multicolumn systems. It is demonstrated that long adsorption profiles are likely to occur in the adsorption of organic contaminants from wastewater onto activated carbon, thus favoring the use of multicolumn rather than single-column systems. For two-component adsorption in a multicolumn system, it is shown that more switching periods are needed than in the single-column case before the profiles stabilize, that the stabilized profiles can differ substantially from those found in a single-column system, and that their shape is strongly influenced by the relative concentrations of the components in the feed. ROLAND KLAUS SCOPEThe adsorption of contaminants from fluid streams onto activated carbon is becoming an increasingly important separation method. The use of a single column often gives relatively poor carbon utilization so that, in practice, two or more columns are normally used in series. Although many studies have appeared in the literature on the modeling and simulation of single-column operation, very little has been reported on periodic countercurrent systems. Continuous countercurrent systems have been modeled for film and film plus pore resistance with linear and irreversible isotherms (Kasten and Amundson, 1952; Neretnieks, 1974a, b, and c). Svedberg (1976) reports results for the simulation of periodic countercurrent operation with film plus pore diffusion and a linear isotherm.When more than one component is adsorbed, the shape of the concentration profiles in the adsorber will change radically, giving peaks and plateaus which result from interactions between the adsorbed solutes and cannot be modeled by the assumption of linear or irreversible isotherms.The purpose of the work described here was to simulate multicomponent adsorption on activated carbon in multicolumn periodic operation, since this is the case most commonly found in practice. CONCLUSIONS AND SIGNIFICANCEIt is demonstrated from approximate calculations that for conditions similar to those commonly found in practice, the adsorption profile is so long that the use of a single-column system is likely to be uneconomic. Multicolumn periodic operation is, thus, the natural choice for carbon adsorption systems.Results for single-component adsorption with film and pore diffusion in a two-column system show that for the conditions examined, the concentration profiles in a twocolumn system stabilize rapidly. There is little change in profile shape after the first switch, although there are indications that at lower feed concentrations, the transient phase would be longer.For the two-component system that is simulated with film resistance, the concentration profiles take much longer to stabilize and can change profoundly with changes in the relative concentration of the components in the feed. The simulations show that as a result of the displacement phenomenon occurring in a multicomponent adsorption, the relative concentrations of components i...

There is an equivalence between stiff and singularly perturbed systems of ordinary differential equations. This feature is exploited in this paper by numerically employing recent singular perturbation methods to attack troublesome boundary layer stage of the solution in which some variables have very short response times. The numerical method affords a means of essentially determining the thickness of this boundary layer. The algorithm is capable of high stability and accuracy for the commonly occurring stiff system, whether or not it is in singularly perturbed form. Application to a singularly perturbed reaction system and a highly stiff reactor system not in singularly perturbed form demonstrate the effectiveness and utility of this approach. SCOPEMany commonly occurring physical and chemical dynamic systems have widely separated time constants. CONCLUSIONS AND SIGNIFICANCERecognition of the equivalence of stiff and singularly Perturbed equations makes available new tools for the solution of both forms of equations. Jn this study, use is mad9 of sineular perturbation methods to develop a numerical technique capable of high stability and accuracy. A unique feature preTent is the ability to monitor the contribution of the stiff component to assess when Page 368 March, 1974 AlChE Journal (Vol. 20, No. 2)the solution is out of the boundary layer. Thereafter the bulk of the transient may be obtained without the accuracy problems associated with this initial section. me numerical approach is applicable to numerous problems in chemical engineering and other disciplines where currently inadequate solution procedures are employed.